As a resonator used in the microwave or millimeter-wave band, a hairpin resonator disclosed in Japanese Unexamined Patent Application Publication No. 62-193302 is known. The hairpin resonator has an advantage that it can be formed to be smaller than resonators using a linearly-extending conductor line.
A planar-circuit-type multiple C-ring resonator formed by means of a thin-film micro-fabrication technique is disclosed in Japanese Unexamined Patent Application Publication No. 2000-49512. The multiple C-ring resonator has an advantage that it has a higher conductor Q-factor than the hairpin resonator disclosed in Japanese Unexamined Patent Application Publication No. 62-193302.
A planar-circuit-type multiple spiral resonator formed by means of a thin-film micro-fabrication technique is disclosed in Japanese Unexamined Patent Application Publication No. 2000-244213. In this type of resonator, currents flowing through respective conductor lines are similar, in distribution, to each other, and thus a further higher conductor Q-factor can be obtained than can be obtained by the hairpin resonator.
Although the multiple spiral resonator disclosed in Japanese Unexamined Patent Application Publication No. 2000-244213 has the advantage that it has high conductor Q-factor, a disadvantage is that it needs high cost to produce it by means of a thin-film micro-fabrication process. When it is required to reduce the size of the resonator, finer fabrication is required, and the production cost is accordingly increased.
Accordingly, it is an object of the present invention to provide a resonator, a filter, a duplexer, and a communication apparatus, which have a small size and a high conductor Q-factor and which can be produced at reasonably low cost.